Sulfuric acid sweetening of straight run petroleum distillates



SULFURIC'ACID SWEETENING F STRAIGHT RUN PETROLEUM DISTILLATES Herv Maz,letit Conronne, France, assignor to Shell Development Company, New York,N. Y., a corporation of Delaware N Dr win App c o n 15, 1. Serial No.591,542

Claims priority, application France June 22, 1 955 6 claims. tel- M1This invention relates to a method for refining hydrocarbon oils,particularly petroleum distillates, treatment with sulfuric acid.

It is knownthat sulfur compounds, particularly mercaptans, can beremoved from petroleum hydrocarbon oils by contacting the oil withconcentrated sulfuric acid. The mercaptans contained in these oils areextractedby the sulfuric acid and react therewith to form disulfides.The latter are soluble in sulfuric acid, but still more soluble in oil,and can only be extracted and removed from the hydrocarbon oil in thepresence of a considerable amount of acid, as is the case with the alkylmonosuliides which are frequently present. If it is desired only tosweeten an. oil, i .e to remove the mercaptans from the oil So that itgives a negative reaction to the doctor test, the treatment requiresrelatively little acid. In this case most of the disulfides and othersulfur compounds re ma n the i The u ur a i t t ent i of particularadvantage in desulfurizing or sweetening hydroarbon l ob n d by s aht-fun d s at n-Q c d oil and boiling below the lubricating oil boilingrange as these distillates contain no or virtuallyno olefinic hydrocarbons which under he influence of concentrated sulfuric acid rapidlyform polymers which have to be removed by a separate treatment.

However, sulfuric acid sweetening of even straight-run petroleumdistillates has often been precluded in commercial practice because ofstill another difliculty. This is that such distillates often containtertiary mercaptans and, when these compounds are present inconcentrations even as low as about 000.04% by weight mercaptan sulfur,contacting the distillate with sulfuric acid heretofore has resulted inthe formation of free sulfur and other highly corrosive forms of sulfurwhich remain in the product. Besides making the product corrosive, thisis especially deleterious in the case of gasoline because it greatlyreduces tetraethyl lead anti knock efiectiveness, i.e., the leadsusceptibilty .of the product. Any aftertreatment of the product toremove this type of sulfur is too complicated and expensive to becommercially feasible.

It is accordingly a principal object of this. invention to provide animproved process for the refining of hydrocarbon oils by treatmentthereof with sulfuric acid. A:

fantasia Patented Nov. 10, 1959 more particular'object is to provide animproved process for the sulfuric acid sweetening of petroleumstraightrun distillates boiling below the lubricating oil boiling range.Still another object is to provide a process for sweetening suchdistillates which contain tertiary mercaptans, wherein the formation offree sulfur and other highly corrosive forms of sulfur is lesssened oravoided, and other advantages are obtained. Other objects will beapparent in the description of the invention.

It has now been found that these and other objects are accomplished bytreating a petroleum straight-run distillate hydrocarbon oil which boilsbelow the lubricating oil boiling range and which contains tertiarymercaptans by adding thereto a small amount of a bromine- ,reactiieunsaturated hydrocarbon material, to be described below in moreparticularity, and thereafter conacting the oil with a relatively smallamount of sulfuric acid.

The petroleum hydrocarbon distillate oils treated by the process of theinvention are tertiary mercaptan-containing fractions obtained bystraight-run distillation of petroleum crude oil. These fractions areessentially free from aliphatic unsaturation such as is present inolefinic and acetylenic compounds or either acyclic or alicyclicstructure. Any bromine absorption by such fractions in a bromine numberdetermination, above an amount equivalent to a bromine number of about1, is due to non-addition type of reaction such as is obtained withcertain higher boiling aromatics. Cracked hydrocarbons, or otherfractions containing aliphatic unsaturation equivalent to a brominenumber above about 1, cannot be suitably treated by this process becausesuch oils contain large quantities of olefins which form gums, polymers,resins, and the like in the presence of sulfuric acid. Thus, the yieldof treated product from cracked oils would be low and the product wouldbe contaminated with undesirable material. The suitable distillates arealso normallyliquid fractions which boil below the boiling range ofening of the middle range distillates such as white spirit or mineralspirits, kerosene, and aviation turbine fuels,

i.'e., those which boil within the range of about C. to

about 315 C. Treatment of such distillates according to the inventionresults in greatly reduced total sulfur content of the product ascompared to conventional sulfuric acid treatment of such distillateswithout the prior addition of bromine-reactive unsaturated hydrocarbonmat r al.

The bromine-reactive unsaturated material which, ac-

cording to the invention, is added to the hydrocarbon distiliate beforethe sulfuric acid contacting step can be a single unsaturatedhydrocarbon compound or a mixture of a number of such compounds and mayor may not contain other hydrocarbons. It should not contain anysignificant amount of non-hydrocarbon material. Especially useful arecatalytically or thermally cracked petroleum fractions, such as lightand heavy normally liquid cracked distillates and the normally gaseousolefinic petroleum fractions such as ethene, propene, butenes, andmixtures thereof with saturated hydrocarbons of the same average carbonnumber such as cracked petroleum gas. Acetylene and other acetylenichydrocarbons containing triple bonds are also suitable. In thisconnection, the term bromine-reactive unsaturated hydrocarbon materialis used herein to include hydrocarbon material which contains one ormore compounds which have at least one bromine-reactive (i.e., byaddition) double or triple bond and may have a plurality of such bondsin either conjugated or non-conjugated positions, in addition to anynon-bromine-reactive, resonating type of unsaturation such as thattypified by the benzene ring. They are thus materials which containaliphatic unsaturation, including olefinic and acetylenic compoundswhich can be either acyclic or alicyclic.

The suitable unsaturated materials have bromine numbers of at least andpreferably at least 30, corrected for any bromine absorption not due toaliphatic unsaturation. In the case of normally gaseous unsaturatedmaterial such as acetylene, propene, etc., the calculated bromine numberis adequate for this criterion. For example, since acetylene has onetriple bond and can therefore theoretically add two moles of bromine,the calcu lated bromine number (grams of bromine per 100 grams ofacetylene) is 1230. As long as the bromine number is at least asindicated above, the unsaturated material will contain a sufficientconcentration of unsaturation to bring about the advantages of theinvention. The unsaturated material must have a boiling point or boilingrange which does not exceed 400 C., and preferably does not exceed 315F. Light cracked distillates having end boiling points (ASTM D86) notgreater than about 225 C. give especially good results.

The amount of bromine-reactive unsaturated material added to thetertiary mercaptan-containing oil to be sweetened must be at least 0.1%by weight of the oil. Less than this amount, especially in the case ofunsaturated material having bromine numbers in the lower part of theoperable range described above, will not adequately reduce the formationof free sulfur and other highly corrosive forms of sulfur. An amount ofat least about 0.5% by weight is preferred. On the other hand, theamount of the unsaturated material added must not be greater than 4% byweight, and preferably not greater than 3% by weight, of the oil to betreated since greater amounts than this give rise to the formation ofgums, polymers, resins and the like to an extent that wouldsignificantly contaminate the treated product. In the case of lightcracked distillates, 1% by weight is ordinarily the most that need beused. Heavy cracked distillates and normally gaseous fractions orcompounds containing bromine-reactive unsaturation are generally used inamounts above 1% by weight of the oil to be treated.

The addition of normally gaseous unsaturated material can beaccomplished merely by dissolving it in the oil to be treated. The useof pressure is not necessary.

The sulfuric acid suitably used in the present process has aconcentration of at least 85% by weight, and preferably at least 93% byweight. The amount of acid used is from about 0.1 to about 10% by Weightof the oil to be treated. Within this range, it is preferred to use atleast 1% by weight, and best results are usually obtained when no morethan 5% by weight, especially no more than about 3.5% by weight, isused.

The technique used in contacting the oil and acid is not critical to theinvention. In general, techniques heretofore used in conventionalsulfuric acid treatment are equally applicable in the present process.Thus the total required amount of acid can be applied to the oil in asingle step, or fractions of the total required amount can besuccessively added until the total is supplied, with or withoutintermediate oil and acid phase separation steps. The type of mixing canbe either mechanical, such as with a paddle or propeller mixer or aturbo-mixer or a circulating pump, or it can be by air or inert gasagitation. A mechanical method or agitation with a nonoxidizing gas ispreferred, however, since this will result in a product which has bettercolor and odor stability. The contacting can be either batch orcontinuous. The time of contact between the oil and acid should besufficient for the sweetening process to be completed, i.e., for theproduct to be negative to the doctor test, but it should not be extendedsubstantially beyond this since needlessly prolonged contact results inpoor product color and odor. Generally, the sweetening reaction iscomplete within 15 minutes to 2 hours, depending upon the particular oilbeing treated.

After the sweetening reaction is complete, the oil must be separatedfrom the acid phase, which at this point is acid sludge. This isconveniently done by settling or centrifuging, or by the addition of anabsorptive solid to the mixture or by percolation of the mixture througha bed of sand or gravel or other filtering material, or by waterwashing. The process of the present invention results in products whichordinarily need no further treatment. However, if desired, the productcan be given a finishing treatment such as distillation to recover theproduct as a distillate, or contacting with clay or other adsorbent.

Not only is the formation of elemental sulfur prevented in the processof the invention but also the reaction time and the amount of sulfuricacid necessary for sweetening are reduced. Irak white spirit was treatedaccording to the invention to give a negative doctor test by means of2.5% by weight of sulfuric acid of 96.7% by weight concentration,whereas without the addition of olefins 3 or 3.5% by weight of acid wasrequired, the duration of treatment being identical. On the other handwith 3% by weight of sulfuric acid of 96.7% by weight by adding 0.6% byweight of a light cracked distillate an Irak white spirit was obtainedwhich after 25 minutes gave a negative reaction to the doctor test, aresult which was only obtained after minutes without the addition oflight cracked distillate.

The process according to the invention is generally carried out atambient temperature. If the temperature is increased, a negativereaction to the doctor test is ob tained more rapidly, but there is agreat risk of free sulfur formation.

Tests have also been made for treating hydrocarbon oils in severalstages by mixing each time with 0.5% by weight of sulfuric acid andadding each time 0.1 to 0.2% by weight of light cracked distillate. Byoperating in this manner the product sometimes contained free sulfur.However, by adding the whole quantity of cracked distillate beforehandgood results are obtained.

The presence of elemental sulfur and other corrosive forms of sulfur isshown by the Mercury Corrosion Test (A.S.T.M. method D268). This test iscarried out by snakin in a closed tube cc. of oil with 1 cc. of cleanmercury, after which thetube is allowed to stand for 15 minutes. If themercury does not change color as compared to a similar test in which theoil is replaced by distilled water, there is no elemental or otherhighly corrosive form of sulfur; i.e., the test is negative.

I In general, it isfound that oils produced by the process according tothe invention give a negative mercury test. There are, however, cases inwhich, as Example III shows, it is not possible to prevent the formationof elemental sulfur completely. In such cases it is found, however, thatthe result of the mercury test is considerably less positive thanwithout the addition to the oil of unsaturated hydrocarbons.

The invention is, illustrated in the following examples.

EXAMPLE I Different quantities of cracked distillate, viz. 1% and 1.5%by weight of light crackeddistillate and 1% and 1.5% by weight of heavycracked distillate were added respectively to four samples of Irak whitespirit containing tertiary mercaptans and having a boiling range of 145C. to 183 C., a specific gravity-of 0.773 and a mercaptan sulfur contentof 0.038% by weight. Each sample was then mixed with 3% by weight ofsulfuric acid of 96% by weight concentration. After stirring vigorouslyby means of a mechanical stirring device, and settling to separate thehydrocarbon from the sludge formed, the samples with respectiveadditions of 1 and 1.5% by weight of light cracked distillate and with1.5% of heavy cracked distillate were found to give a negative doctortest and a negative mercury test, as is shown by 5 spirit is alsoobtained which shows a negative mercury test; the stability of the odorand color is, however, not as good. 7

I EXAMPLE II 300 tons of a tertiary mercaptan-containing Irak white 10spirit with a mercaptan sulfur content of 0.0144% by weight and a totalsulfur content of 0.09% by weight were treated five to seven times with0.2 to 0.5% by weight of sulfuric acid (96% by weight) after previousaddition of 0.6% by weight of cracked distillate having a boiling rangeof 40 C. to 183 C. and a bromine number of 5 6. The results are shown inTable II.

Table II Test No 1 w 2 3 v Quantity of cracked distillate added, percentby weight 0.6 0.6 0.6 Number of additions of His 5 6 7 Total amount ofsulfuric acid (96% by w ht) added, percent by weight 1 3.5 3. 5 Durationof treatment in hours 25 32 "Doctor test neg. neg. neg. Mercury testneg. neg. neg. Total sulfur content of product, percent by weight 0. 040. 03 0. 03

EXAMPLE III When the white spirit thus treated is stored in light for 60days, neither its color nor its odor deteriorates."

By repeating the'above tests, mixing beingefiected by means of airinstead of by mechanical means, a white In this series of experiments,tertiary mercaptan-containing hydrocarbon oils listed in Table II werecontacted with sulfuric acid after addition of unsaturated material aslisted in Table IV.

35 the data in Table I. The fourth sample, treated with T bl 111sulfuric acid after the addition of 1.0% by weight of heavy crackeddlstlnat?) gave 135 mercury Petroleum Fraction Gasoline White KeroseneGas oil The control sample which was treated with sulfuric acid in asimilar manner, but to which no unsaturated material 40 1Specificgravity at 15 C... 0. 740 0. 777 0.803 0.834 had been added gavea Posm"e mercury test; Boiling rangein0 100150 150-185 200-200 200-300The data of Table I also show that the duration of the Mercury test 05-mg? 1 P Total sulfur content, percent operation is considerably reducedby adding cracked by weight 0.030 0.150 0.200 0.83 distillates.

Table I White spirit White spirit treated with sul- Treatmentwithtreated with furic acid after the addition sulfuric acid of heavy orlight cracked dis-' only tillate Light cracked distillate, percent by,,weight 1. 0 1. 6 Heavy cracked distillate, percentby weight 1. 0 1. 5Sulfuric acid, percent by weight 3.0 3.0 3.0 3.0 3.0 Mixing time inminutes... 45 45 30 Doctor test neg. neg. ne ne ne Mercury test, ASTM/D268... pos neg. neg. pu neg. Color Lovibond after days 0.75 0. 5 0. 50.5 0. 5 Odor H... fairly good fairly fairly good fairly good good goodTable IV Light Light Light Light Light I eat. eat. eat. eat. thermalUnsaturated Hydrocarbon cracked cracked cracked cracked crackeddistillate distillate distillate distillate distillate I II III IV-Specific gravity at 15 0 0. '73'1 0. 037 0. 719 0.738 0. 749 Boilingrange, C 41-144 20'47 68-94 41-205 51-179 Bromine number 57 132 103 86.5 70 Maleic anhydride numbe 30.2 28.4 46.3 6 3 Total sulfur content,percent by Weight 0.031 0.065 0.047 0.150 0.067 Mercury test.. neg. neg.neg neg neg.

7 Table V summarizes the results of the treatment according to theinvention of the distillates referred to in Table III after addition ofthe light cracked distillate I shown in Table IV.

8 Table VII shows clearly that although the sweetening reaction proceedsmore quickly at higher temperatures, the mercury test gives a positivereaction at even 30 C. Since the object in View, which is to prevent theforma- T able V Petroleum fraction treated Gasoline White spiritKerosene Gas oil Light catalytic cracked distillate I, percent by weight0. 6 1.0 0 0. 6 1.0 0 0.6 1.0 0 0. 6 1.0 Sulfuric acid, percent byweight 3 3 3 3 3 3 3 3 3 3 3 Time required to obtain a negative doctortest, in minutes 50 30 30 70 35 40 80 60 70 6 55 60 Mercury test pos.neg. neg. pos. neg. neg. pos. neg. neg. slightly slightly neg.

pos pos.

Total sulfur content 0. 023 0. 024 0. 027 0. 042 0. 029 0. 018 0. 195 0.159 0. 131 0. 770 0. 736 0. 732 Color Lovibond 0.5 0.5 O. 0. 5- 0. 5- 0.5- 0. 75- 0. 75- 0. 75- 3. 5- 3. 5 3. 5-

tion of elemental sulfur, is not attained in this way, the

use of a temperature which is higher than about 20 or C. is usuallyinadvisable. While not usually necessary, the acid and oil can becontacted at a reduced temperature, e.g., l0 to +10 C., if desired.

Table VI gives the results of the treatment of the white spirit of TableIII with sulfuric acid, with prior addition of the unsaturatedhydrocarbons referred to in Table IV. Table VI also shows the resultsobtained by using as unsaturated hydrocarbons cracked gases andacetylene.

Table VI Percent by Time required Total sulfur Unsaturated wt. of toobtain a content of Unsaturated hydrocarbon added hydrocarbon, sulfuricacid Color, negative Mercury test white spirit percent by of 96.7%Lovibond doctor test, after treatwt. by wt. minutes ment concentration 370 0.041 3 0. 5- 45 0. 022 Light cat. cracked distillate I 3 0. 5- 0.0273 0. 5- 0.020 Light cat. cracked distillate II 3 0. 5- 35 neg 0.021Light cat. cracked distillate III..- 3 0 5- i5 slightly pos--. 0. 024 3r. 5 pos Light cat. cracked distillate IV 3 Slightly 0' 025 3 0 pos rLight thermal cracked distillate 3 0. 5 4g slighzly pos 0.022 3 5 0Cracked gas poor in unsaturated com- 3 O 0 032 pounds, washed with NaOH,Schilling 3 030 density=1.1. Cracked gas rich in unsaturated corn- 3 0.5- 0. 038

pounds, washed with NaOH, Schilling gergiity=2.4, Specific gravity at 15O.=

.D Acetylene 1.5% by 3 0. 5- neg 0.039

volume.

I claim as my invention: 1. In the process of sulfuric acid sweeteningof a straight run petroleum hydrocarbon distillate having an Accordingto the data in Table VI the hydrocarbon oils treated according to theinvention do not all give a clearly negative mercury test. However, aconsiderable improvement is nevertheless obtained as compared to theconventional sulfuric acid treatment without prior addition ofunsaturated material.

EXAMPLE IV This example shows the eflect of temperature on the treatmentof tertiary mercaptan-containing Irak white spirit according to theinvention. The unsaturated hydrocarbon used was the light catalyticcracked distillate I referred to in Table IV of Example 111. The resultsof the tests are given in Table VII.

end boiling point no higher than about 400 C. and containing tertiarymercaptans which normally form free sulfur during the sulfuric acidsweetening process, the improvement which comprises reducing said freesulfur formation by adding to the untreated distillate from about 0.1 toabout 4% by weight of a bromine-reactive unsaturated hydrocarbonmaterial having a bromine number of at least 10 and boiling no higherthan 400 C., and thereafter contacting the distillate with from 0.1 to10% by weight of sulfuric acid having a concentration of at least byWeight.

2.. A process according to claim 1, wherein the bromine number of theunsaturated hydrocarbon material is at least 30.

3. A process according to claim 1, wherein the brominereactiveunsaturated hydrocarbon material is a cracked petroleum fraction havingan end boiling point no higher than 225 C., and the amount ofunsaturated hydrocarbon material added is no greater than 1% by weightof the distillate.

4. A process according to claim 1, wherein the bromine- 10 6. A processaccording to claim 5, wherein the distillate is an aviation turbine fuelfraction.

References Cited in the file of this patent UNITED STATES PATENTS1,791,521 Bjerregaard Feb. 10, 1931 2,068,850 Ellis Ian. 26, 19372,341,487 Taylor et al. Feb. 8, 1944 FOREIGN PATENTS 639,137 GreatBritain June 21, 1950

1. IN THE PROCESS OF SULFURIC ACID SWEETENING OF A STRAIGHT RUNPETROLEUM HYDROCARBON DISTILLATE HAVING AN END BOILING POINT NO HIGHERTHAN ABOUT 400* C. AND CONTAINING TERTIARY MERCAPTANS WHICH NORMALLYFORM FREE SULFUR DURING THE SULFURIC ACID SWEETENING PROCESS, THEIMPROVEMENT WHICH COMPRISES REDUCING SAID FREE SULFUR FORMATION BYADDING TO THE UNTREATED DISTILLATE FROM ABOUT 0.1 TO ABOUT 4% BY WEIGHTOF A BROMINE-REACTIVE UNSATURATED HYDROCARBON MATERIAL HAVING A BROMINENUMBER OF AT LEAST 10 AND BOILING NO HIGHER THAN 400* C., AND THEREAFTERCONTACTING THE DISTILLATE WITH FROM 0.1 TO 10% BY WEIGHT OF SULFURICACID HAVING A CONCENTRATION OF AT LEAST 85% BY WEIGHT.